For more than a year now, english members were badly redirected to french side of the website, right after sign in.
So what you had to do after was to switch language using the little flag in the upper right corner of the screen to get english language back.
But as I recently removed the language flag once signed in, you were no more able to switch back to english.
Sorry about that, I'm really surprised nobody told me sooner about that issue.
A friendly member pointed it out to me and I managed to reproduce the problem quickly.
After few hours scratching my head and looking for a good solution, I released only a partial fix.
You should now be able to stay in english once signed in.
What the system did before was : After sign in, language choosen was website's default language (french indeed).
What the system does now : After sign in, language choosen is the same as the current browser's one.
But the logical aim would be to use user's front-end choice, regarding member's profile preferences.
I'll give you more feedback when it will be definitively fixed.